Investigations will be pursued in several related areas: 1. Rejoining of DNA strand breaks in Chinese hamster ovary cells following low doses (less than 1000 rads) of X-rays (using reorienting-gradient zonal ultracentrifugation). 2. Effects of hyperthermic exposure on the rejoining of DNA strand breaks in Chinese hamster ovary cells following low doses (less than 1000 rads) of X-rays. 3. Effects of hypo- and hyperthermic exposures on the survival of the very radiosensitive murine leukemic lymphoblast, L5178Y S/S, as a function of cycle position. 4. Rejoining of DNA strand breaks in L5178Y S/S cells as a function of cycle position.